An outsole is an exposed portion of a sole structure on the bottom of a shoe. Because an outsole may contact the ground when a wearer of the shoe walks, runs or otherwise moves about, it is common for an outsole to include various types of features. Examples of functional features include lugs and other types of traction elements. Other examples may include grooves, sipes or other types of recesses formed in an outsole so as to increase traction or flexibility of a sole structure.
Outsoles are typically formed by molding one or more pieces of outsole material such as synthetic rubber. An outsole mold normally has features that correspond to features that will be formed in a molded outsole. For example, a mold may include various depressions that correspond to outsole lugs, may include ridges that correspond to outsole grooves, etc. Outsole molds can be fabricated in various ways. As one example, a mold may be cast from molten metal. A plug made from sand or other silicate material and having the outsole contours may be used to cast the outsole mold. The plug may be created from an outsole master, a metal component having the same shape and features as the outsole. An outsole master is normally machined from a larger piece of metal.
Other types of footwear sole structure components may also be molded. For example, many types of footwear include a separate midsole. In many shoe designs, one or more side edges of a midsole may be exposed in a completed shoe. Some designs may also expose bottom regions of a midsole, e.g., through openings in an outsole. Midsole molds may be fabricated using techniques similar to those used to fabricate outsole molds.
It is known to form outsole masters having textures on surfaces that correspond to exposed surfaces of an outsole modeled by the master. Such textures may include surface features having a heights and/or widths that are too small to form efficiently through conventional machining techniques. Chemical etching is conventionally used to create such textures. Chemical etching requires use of highly caustic materials to chemically erode metal from surfaces of a master. Such chemicals are toxic and can be dangerous to handle. It may also be difficult to dispose of such chemicals in an environmentally responsible manner. Moreover, and apart from safety and environmental issues, there are limits on the quality of surface treatments achievable through chemical etching. For example, chemical etching tends to create rounded edges. It can thus difficult to chemically etch surface features with crisp lines and various other types of surface details.